The High-temerature Oxidation Property Of Ultra-supercritical Steam Turbine Blade Steel

Modern thermal power plant improves their efficiency by raising steam parameters (main steam temperature and pressure), which puts forward the turbine blade materials with a higher heat-resistant, thus new blade materials have been constantly developed and applied. According to the working conditions, heat-treatment as well as high temperature oxidation experiment were carried out for newly introduced 1Cr11MoNiW1VNbN heat-resisting steel used in ultra supercritical steam turbine blade. A comprehensive evaluation in its resistance to isothermal oxidation performance were given in this paper.According to GB/T13303-91 and HB5258-2000, High temperature oxidation experiments were conducted both at 700℃for 1000h (thermostatic) and for 600h(11 times thermal cycle were induced) by static discontinuous method. Gravimetric data, corresponding to specimen mass increment per surface unit, were collected. The time-dependent changes in the complex structures and phase of scales were determined using scanning electron microscope, X-ray diffraction and eds analyses. Oxidation kinetics and failure analysis of scale were also studied.The experiment results were summarized as follows:the optimum heat treatment process is determined, quenching temperature 1150℃, tempering temperature 710℃, under the premise of 1Cr11MoNiW1VNbN steel used around 700℃; its mechanical performance accorded with standard after heat-treatment, and the steel is in antioxidant levels after isothermal oxidation at 700℃for 1000h. The oxidation film can be divided into (Fe,Cr)2O3 outer layer, mixing layer (anaerobic zone+(Fe,Cr)3O4) and(Fe,Cr)2O3 lining layer. Besides, the (Fe,Cr)2O3 chips grows on the surface. The oxidation kinetic curves follow parabolic rate law with the steady growth of chromium rich scale. While, because of the rapid growth of Fe2O3 and crack flake on scale, oxidation change into linear law. A second breakaway oxidation appered in the last period, the thickness of film increased significantly, and no evidence of spalling up to 1000h.Anomalous time dependence of scale integrity during oxidation of steel in the time range 600-1000h. It was obvious that the extent and morphology of the inscale pores, oxidation film degradation, alloy elements depletion in matrix and the thermal stress were of great importance for the spalling characteristics of scale, while has to do with the film thickness.